1. Field of the Invention
The present invention relates to an apparatus for forming a packaging unit consisting of an endless hose or for sealing a prefabricated packaging unit, in particular a bag for loose material, said apparatus comprising an ultrasonic welding device including an anvil and a sonotrode, which are movable towards each other, and a means for positioning the hose material to be welded between the anvil and the sonotrode, The present invention additionally relates to a method for forming and/or sealing a packaging unit.
2. Brief Description of the Prior Art
An apparatus according to the generic clause as well as a method are described in the article xe2x80x9cVerschliexcex2en mit Ultraschallxe2x80x9d (xe2x80x9csealing with ultrasoundxe2x80x9d) of the applicant of the present patent application in the periodical xe2x80x9cVerfahrenstechnikxe2x80x9d 34 (2000), No. 12, pp. 12-13. This article describes various ultrasonic welding devices, e.g. for welding a valve bag in the area of its valve, said valve bag being first pushed onto a filler neck, filled with a loose material, and, subsequently, it is removed from the filler neck. These valve bags are prefabricated packaging units which are sealed in the above-described apparatus.
An ultrasonic welding device is, however, also known for forming a packaging unit consisting of an endless hose. In the so-called FFS (form-fill-seal) method a gusset-type hose or a hose without a gusset is unwound from a roll. A predetermined length piece is cut off from the endless material supplied, and sealed at the location of separation by conventional welding. The thus produced bag for loose material, which is open at the top, is first deposited in a place of intermediate deposit. Here, the weld cools down so as to achieve the strength which is necessary for the future filling of the bag for loose material. The prepared bag for loose material is then seized in said place of intermediate deposit and placed below a filling unit such that its opening faces upwards. After the filling operation, the material of the bag for loose material is welded also on the upper side of the bag. For this purpose, the above-mentioned prior art provides an ultrasonic welding device.
This known device used for carrying out the FFS method is, on the one hand, disadvantageous insofar as a place of intermediate deposit is required. On the other hand, the bag for loose material produced according to the FFS method has, at least on the lower side thereof, a length section of the hose material projecting beyond the lower weld at the end of the bag. It should be the aim of the method to produce the highest possible number of bags for loose material from the endless hose material supplied.
In the case of the above-described apparatus for sealing a valve bag after removal of said valve bag from the valve neck, the problem arises that particles, e.g. pigments or toxic particles, may adhere to the inner side of the valve. The particles located between the free end of the projecting valve and the weld may dust off during future handling. This cannot be desirable in the case of toxic substances. Paint pigments dusting off lead to a very intensive colouring of the surroundings, which is not desirable either.
It is the object of the present invention to provide an apparatus of the type mentioned at the start, in the case of which the above-described problems do not exist. For the so-called FFS method, for example, an apparatus is to be provided by means of which the endless material supplied is utilized in the best possible way for producing the bags for loose material. In addition, particles adhering to the valve are to be prevented from dusting off. Hence, it is, in particular, the object of the present invention to further develop the apparatus mentioned at the start in such a way that it can be used for producing packaging units in the case of which length pieces projecting from the weld at the end of respective packaging unit are avoided as far as possible.
It is a further object of the present invention to provide a method in the case of which the endless material supplied is utilized in the best possible way for producing packaging units. Furthermore, the method aims at preventing particles, which adhere to the sealed packaging unit, from dusting off.
For solving the problem as far as the apparatus is concerned, the apparatus mentioned at the beginning is further developed by means of the present invention insofar as the anvil comprises two anvil parts which are movable relative to one another in the direction of the sonotrode, one of said anvil parts being implemented as a sealing anvil and the other part being implemented as a separating anvil.
By means of the apparatus according to the present invention, it is possible to effect sealing and, simultaneously, cutting off directly in, or adjacent to the weld produced by means of ultrasonic welding. The apparatus for sealing especially a valve bag, cuts off the free end, which projects beyond the valve bag, in or directly adjacent to the weld produced by means of ultrasonic welding. It follows that contaminations adhering to the outwardly open residual piece of the valve neck are removed, e.g. sucked off, together with the projecting end piece already at the filling station.
When forming packaging units, in particular bags for loose material, according to the FFS method, the endless material supplied is utilized in the best possible manner by means of the apparatus according to the present invention. The lower end of the bag for loose material is defined by the weld. A length piece of the hose material projecting downwards from said weld does not exist.
For simplifying the structural design of the apparatus according to the present invention, it is suggested that, in accordance with a preferred embodiment, the two anvil parts should essentially be implemented as plate-shaped components, and that the anvil parts should abut on one another with their neighbouring longitudinal sides. The relative movement of the two anvil parts is thus preferably guided via the neighbouring longitudinal sides.
Neat and reliable cutting off of the projecting valve piece as well as cutting off of the predetermined length piece from the endless hose supplied for forming an open bag are supported by the circumstance that the separating anvil is implemented such that it tapers in the direction of the sonotrode.
In particular in cases in which gusset-type hoses are used for producing packaging units, and for the purpose of sealing valve bags, it turned out to be advantageous when the sealing anvil is provided with a pressure surface extending parallel to the end face of the sonotrode, said pressure surface being provided with diagonally intersecting grooves which are distributed over the area thereof. The use of gusset-type hoses entails the problem that four layers have to be welded at the edges of the hose, whereas in the middle only two layers have to be welded. In particular at the transition from the two-layered to the four-layered area, the material of the packaging unit, which is preferably plastic material at least in the area of the weld, should be able to flow to such an extent that the differences in the wall thicknesses can be compensated for. This effect is preferably produced by grooves which are formed on the pressure surface in a diagonally intersecting pattern. The dimensions and the depth of the grooves depend on the thickness of the material used and on the nature of the packaging unit. The depth of the grooves increases when larger wall thickness are used.
In order to simplify the apparatus according to the present invention, it is suggested that at least the sealing anvil should be implemented as an integral component extending over the whole welding length. Surprisingly enough, it turned out that, even in the case of the FFS method, a gusset-type hose can reliably be sealed across its whole width by means of an apparatus having such a simple structural design.
The material to be sealed can be clamped prior to and cut off subsequently to the sealing process more easily in view of the fact that both the sonotrode and the anvil are adapted to be moved towards each other.
For sealing valve bags in the area of their valve after the filling operation, the ultrasonic welding device should be designed so as to obtain the best possible outward appearance of the bags. This means that, when seen in the direction of removal of the bag, the ultrasonic welding device should be arranged before the front end of the filler neck in such a way that the valve projecting laterally beyond the valve bag is in any case welded on the level of the longitudinal valve bag side located adjacent the valve neck, and the free, projecting end of the valve bag is cut off on said level. In accordance with this preferred embodiment of the apparatus according to the present invention, the weld for the valve is produced such that it is located approximately in the same plane as the longitudinal side beyond which the valve projects prior to the filling operation. Also the free end of the valve, which is located directly adjacent the weld, is arranged approximately in the above-mentioned plane. It follows that the sealed valve bag produced in this way has a rectangular contour, when seen in a side view; this type of contour is preferred, especially when the sealed bags are stacked and when a large number of stacked bags is enveloped by means of winding, stretching or shrinking later on.
For solving the problem as far as the method is concerned, the method known e.g. from the above-mentioned article xe2x80x9cVerschliexcex2en mit Ultraschallxe2x80x9d is further developed by the present invention insofar as the material of the endless hose or of the packaging unit projecting beyond the weld is cut off directly adjacent to or in said weld. In the sense of the present invention, xe2x80x9cdirectly adjacent to the weldxe2x80x9d means that the projecting material is cut off directly at the edge of the weld. It follows that all the surfaces which project beyond the weld and to which loose material that may perhaps dust off may adhere are removed when the projecting material is being cut off. It follows that it will not be possible that material dusts off from the packaging unit which is in principle closed.
If cutting off is effected in the weld, the hose-shaped residual piece of the valve is closed on one side thereof, by way of example; this will also reduce the risk that particles dust off from this cut-off part of the valve bag. It is e.g. imaginable that, in the case of highly toxic particles or particles having a strong colouring power, the projecting end is, one the one hand, sealed in the area of the weld to the packaging unit by carrying out a cut in said weld and that, on the other hand, the front, outer end of the valve, which is first pushed onto the filler neck, is sealed through other effective measures, e.g. by ultrasonic welding; this sealing should, as far as possible, be effected before the projecting material is cut off. It follows that a hose section of the valve, which is sealed on both sides, is cut off from the packaging unit. In accordance with this preferred embodiment, particles cannot dust offxe2x80x94neither from the sealed valve bag nor from the residual piece that has been cut off.
If the method according to the present invention is used for forming packaging units from an endless hose, the endless material, which is supplied for this purpose cyclically and in the form of identical length sections so as to form identically sized packaging units, is utilized in the best possible way. An edge projecting outwards beyond the weld will not exist, provided that the projecting material is cut off directly adjacent to the weld. A location of separation produced in this way forms the opening for the packaging unit cut off from the endless hose in the next step. Even in cases in which packaging units are produced from an endless hose supplied, it is possible to cut off the projecting material in the weld. In accordance with this preferred embodiment, two packaging units are sealed on at least one side thereof, when the endless material is welded at the location in question. This will increase the rate of production of prepared packaging units.
In the case of the method according to the present invention, the projecting material can be cut off by any cutting means, e.g. also by a blade which is adapted to be moved along the location of separation to be created. Such a blade will, however, become blunt, when it is used continuously. In accordance with a preferred embodiment of the method according to the present invention, it is therefore suggested that the projecting material should be cut off by means of an ultrasonic pulse. Surprisingly enough, it turned out that, when cutting off is effected by means of ultrasonic welding, the double-layer material of the packaging unit can be cut through without interconnecting the two layers in such a way that a subsequent spreading apart of the layers for subsequent filling of the packaging unit is made impossible. Other than in the case of movable blades, a separating anvil, which is used for cutting off by means of ultrasound, need not be resharpened at regular intervals.
The structural outlay required for producing an apparatus which is suitable for carrying out the present method is reduced still further by the circumstance that, in the case of the method according to the present invention, the projecting material is preferably cut off by at least part of the same ultrasonic device which is also used for producing the weld. For forming the weld and for cutting off the projecting material, identical parts of an ultrasonic device can be used. When the method is executed in this way, the intensity of the ultrasonic pulse and/or of the contact pressure and the length of the period in which the material is acted upon by the ultrasonic device can be used for controlling whether the opposed layers of the endless material are to be welded together or whether the projecting material is to be cut off.
With respect to the simplest possible control of the ultrasonic device, it should, however, be preferred to use for the welding as well as for the cutting operation a common sonotrode as part of the ultrasonic device, whereas, for the purpose of cutting, a separating anvil should be pressed against the sonotrode and, for the purpose of welding, a sealing anvil should be pressed against the sonotrode, the material being positioned between the sonotrode and the respective anvil.
If the method according to the present invention is used for sealing prefabricated packaging units which consist of a valve bag, an end-piece-free peripheral surface can be formed in accordance with a further preferred embodiment, provided that the valve projecting laterally beyond the valve bag is cut off at a point located on a vertical applied to the longitudinal side of the upright valve bag, or behind said vertical when seen in the direction of the valve bag. In the prior art, the projecting valve is cut off at a point located outside of an envelope applied to the filled side faces of the upright valve bag. The rest of the valve remaining on the valve bag will therefore project beyond the sealed valve bag in the form of an end piece. It follows that, when the bag is mechanically conveyed via conveying belts, it may happen that the residual rest of the valve is squeezed and tears; in the worst case, it may even be torn off the valve bag. Furthermore, the projecting rest of the valve turned out to be problematic, when a stack, which consists of a plurality of sealed valve bags, is being enveloped by shrink or stretch covers. The residual pieces of the valves sometimes project beyond the outer surfaces of such package stacks and form comparatively sharp edges at which the shrink or stretch cover to be applied tears.
When the method according to the present invention is used, the separating point for cutting off the projecting valve is located on or on the inner side of a vertical applied to the longitudinal side of the upright bag, and, consequently, a sealed packaging unit whose envelope is exclusively defined by the filled side faces of the valve bag is produced by means of the preferred embodiment of the method according to the present invention. A packaging unit which has been formed in this way can easily be conveyed mechanically and it can be stacked so as to form a stack of individual pieces which has a smooth surface.